The effect of plasma nitriding on the fatigue behavior of DIN 1.2210 cold work tool steel

Plasma nitriding is an important thermo-chemical surface treatment which is widely used in order to enhance the surface hardness, fatigue strength and wear and corrosion resistance of steels. In this research, the effects of plasma nitriding parameters including temperature and time on the microstructure and fatigue strength of quenched and tempered DIN 1.2210 cold work tool steel were investigated. The microstructures of base material and nitrided layer were examined in details by optical microscopy and X-ray diffraction (XRD) analysis. Micro-hardness measurements were used to determine surface hardness and case depth. Fatigue tests were performed using a rotating bending machine. The results indicated that the plasma nitriding process led to a considerable increase in the micro-hardness and fatigue strength values. Furthermore, the maximum fatigue strength was attained after plasma nitriding at 550 °C for 6 h, which increased the fatigue life of the specimens by about 67%. It was also found that the dominant fatigue crack initiation mechanism in the plasma nitrided specimens was subsurface ‘fish eye’ type crack formation originated from internal nonmetallic inclusions.